Use of phosphites in esterification reactions of synthetic alcohols



Patented Sept. 30, 1952 UNITED STATES ATENT oFrIcs USE OF PHOSPHITES IN ESTERIFIOAT ION REACTIONS OF SYNTHETIC ALCOHOLS Boyd E.- Hudson, Jr., Cranford, Howard L. Wilson,

' Elizabeth, and Joseph F. Nelson, Railway, N. J.,

assignors to Standard Oil Development Com- 1 pany, a corporation of Delaware No Drawing. Application October 22, 1949, a Serial No. 123,081

5 Claims. 1

This invention relates broadly to a method for preventing color formation in chemical products during reactions and particularly to prevention of color in esteriflcation reactions whereinthere are impurities in the reactants of the type which tend to give undesirable color in the final products.

It has been discovered that very good quality organic esters, useful as plasticizers, can be prepared from impure synthetic alcohol products which normally yield colored ester products by the addition of certain organic phosphorous esters in very small quantities to the esterification reaction. It has been found that phosphites, both the simple esters and-the polyphosphites such Such impurities are ly difficult to remove by conventional means. 7

These impurities either contaminate'the product directly or tend to cause side reactions and by-- products during the reaction period, thus forming further impurities difficult to separate from the final product. Impurities in the final product may give highly undesirable color and may otherwise be unwanted contaminants andat the same time may present extremely difiicult problems of removal. An especially acute purification problem is created by impurities present in chemical intermediates used to prepare pure chemical products such as colorless plastics and resins, very pure dyes, and pure pharmaceuticals and foodstuffs. I

One such problem in purification is found in the manufacture of high purity water clearplasticizers which are especially useful for clear or light colored resins and plastics.

-The ever expandingfluse of plastic materials, especially of the light colored types, including vinyl chloride polymers or copolymers, polyvinyl ,acetate, cellulose esters, ac'rylate and math acrylate resins, rubbers such as the'emulsion copolymers of butadiene with styrene or acrylo nitrile, or the copolymers of isobutylene with small amounts of a diolefin such as isoprene have created a large demand for: suitable plasticizers.

Alkyl esters and particularly -'di-2 ethylhexylphthalate and di-n-octyl phthalate have been known to bev satisfactory plasticizers for -jtha aforementioned high molecular weight materials,

but the supply oftheseplasticizers has been unable to keep pace with the expansion of the plastics industry, largely because of a shortage of alcohols suitable iorthe manufacture 'of the desired esters.

Other types of useful plasticizers are certain new alkyl'esters of polybasicacids, in which the; alkyl groups predominantly contain '8 carbon atoms in a branched chain structure. These can be prepared from certain novel monohydric alip hatic alcohol mixtures, and it has been discovered further that certain synthetic alcohols give esters of unexpectedly superior to comparable esters of this is especially true of' C1; isooctyl alcohols. p I v The alcohol mixtures preferred for use in these new valkyl ester plasticizers are best obtained by the OX0 process. The term Oxo'process is well understood in the art as referringto a process wherein an olefin feed is first reacted or oxo-j natedv with carbon monoxide and hydrogen at a temperature between 250 and 400 F., and under a pressure of about to 400 atmospheresjin' the presence ofa cobalt or similar catalyst, *generally introduced in the form of a fattyacid salt,

to form aldehydes in accordance with the follow The aldehydes s6 form d are then catalytic'ally hydrogenated to form tlie'desired alcohols'as The preferred hydrogenation catalystsare those: of the sulfur sensitivenickeltype though other known hydrogenation catalysts such as the'ksiilfides of nickel, molybdenum and cobalt, v'uth 'or without support on carbomsilica, as; can also be used, especially where, a rugged sulfurinsensitive catalyst. is desired. The basic princi ples and operatingconditions of the .foxojiproci 'ess which can be used for making the desired v'alco- .hols are describedffo'r example infll. S Patent" 2,327,066 and elsewhere.

The over-all carbonylation or so-calledfQxo reaction as outlinedabove, provides a particu-w larly effective method for preparing valuableprimary alcohols, particularly of the C4 to C1 :E

range, which find large markets as intermediates for detergents and plasticizers. The C8,. and Ca OX0 alcohol products are especially preferred; for use in forming esters to be useclas plasti-- cizers in light colored or colorless plastics and resins. The most readily available. olefinie feed for the x0 reaction as outlined above are selected hydrocarbon streams derived from.

petroleumjrefinery sources andthese frequently have sulfur contents as high as 0.1% or even higher. Furthermore, there are a variety of other ways in which sulfur may be introduced into the alcohol product during boththe oxonationand.

hydrogenation stages. For instance, the acids used to form the metal oxonation catalyst for the purpose of introducing the metalinto the re- Any sulfur which is present in the. crude.re--.

action/mixture v containing. the carbonyl loompounds, is carried through the oxonation stage into-the hydrogenation stage where it combines with .the hydrogenation catalyst to reduce. and. ultimately completely destroy its activity unlessv sulfur insensitive catalysts are used. The sulfur sensitive catalystsare generally of the metallic type-and-the deactivating effect of the sulfur on their activity requires frequent reactivation, catalyst replacement, and increased amounts of a.catalyst whose-cost is. definitely acommercial factor. and may beprohibitively high. Thus, itv is.:considered necessary for optimum operation,

in-the hydrogenationstep to employ a..sulfurinsensitive catalyst. These. sulfur insensitive catalystsinclude. particularly certain metallic sulfide hydrogenatingcatalysts, examples of such catalysts' being molybdenum sulfide and tungsten.

sulfide. 7 While thesecatalysts have the decided advantage of avoidingxthe inactivation. due to sulfur. content of the feed stock, they alsov possess the-disadvantage that they permit the sulfur to pass unchanged through the hydrogenation zone and, in'deecLin many cases, tend to introduce additional-sulfur contamination into the alcohol.

Thusgthefinal crude-alcohol may have a total sulfur content from 30 to 100 p. p. m., or, in some cases, anevenhigher valueif no cleanup operations are"d one previously. Veryspecially prepared- 0x0 alcohols may; have sulfur contents in:.the range of 20'p; p. m.

,One of' the largest and most important uses developed for-the synthetic alcohol products is thatof producing esters suitable for plasticizers, byreaction with both. aliphatic. and aromatic acids or ,anhydrides including such examples as.

phthalic acid, maleicacid', adipic acid, and also phthalic and maleicacid anhydrides. Certain plasticizers and particularly for use in clear plastics. These'include alcohols of from C4 to C12 range such as the butyl alcohols, the octanols, arid the nonanols. It has recently been discovcred that synthetic alcohols of the C8 series and chosen? from the isooctyl type are among the esterification alcohols to prepare best type of plasticizers.

These esters are prepared in standard type" esterification equipment employing reactors made of' 'stainl'ess steel or some other structural metal The synthesis gas used .in the- 4 or, in some special cases, in glass-lined reaction vessels.

In a number oflinstances; particularly when the esters were produced in reactors having metallic surfaces exposed to the reacting mixtures, the products were found to be deficient as;-..to the. standards: required for plasticizers, especially in-such characteristics afiected by color and plasticizing qualities such as the poor weathering-tendency .of the resins and plastics in which such. plasticizers are used. These undesirable characteristics including th color are believed to be caused by impurities present in the synthetic alcohol product and particularly by the sulfurproducts present in the alcohol, although other impurity materials can also affect the color including polymerized and condensed higher molecular weight impuritiesas well as unreduced carbonyl. compounds, unsaturated carbonylie.

alcohols is in the form of organically combined. sulfur. Although the type of organic impurities.

in which .the sulfur occurshasnot beeufully determined, it is believed that thesulfur is. press Argenerally deleterii'-' ent in a variety of'forms. ous color-forming, action. takes. placev during esterification whenv sulfur occurs in. the. final. alcohol. Up to the present. invention, it. was.

considered necessary to removethe major portion of 'sulfur' containing compounds fromthe.

finished alcohol by distillation or some other 'of'thesynthetic.alcohols prepared .by the oxona tion'and hydrogenation reaction are known to beespecially suitable for the manufacture of ester.

suitable purifying procedure. 'These. .purificae tions were especially necessary if the ester were manufactured.instainless steel equipment, or excess unreacted .alcohol were recycled. to the esterification zonein. order to obtain..a..crude ester of reasonablygood color whichwould. not

need extensive purification ,prior. to.v inclusion.

in plastics.

Intypical alcohol recycle esterificationoperations,"a 29% molal excess of. alcohol is used based hydride.

sufiicient time. stripped 01? from the ester [product preferably under reduced pressure and blended with. fresh. alcohol for returning to the esterification zone' Thus, undesirable color forming materials have the-opportunity to buildup during the. recycle stages to' a point at whichthey mustbepurged from the system. beforelcontinuingthe. recycling operation. whichoccur even .though theactual: reaction is carried out-in corrosion'resistant or glass-lined equipment. The problem is even more acutewhen thereactionlis carried .outin steel or other metal reactors. .Low temperaturecatalytic es terification' can also: be carried out using an acidic catalystrsuch asabenzene sulfonic acid catalyst; The high temperature esterification 1s;.however, a-much-more severe test as 'to the purity: and: stability of the'reactantsand is more This presents impurity problems:

5. truly representative" of certain plant scale esterification conditions..

.A study of the color formation phenomenon.

has indicated that the color formation is associated with the sulfur content of the isooctyl alcohol.

not even partially removed from the ester ,b'y

topping off the. excess alcohol. and phthalic an-.

The color can be somewhat removed However,

hydride. by vacuum distillation of g the ester.

the distillation of-the isooctyl'phthalates could be completely eliminated if a, satisfactory fcolor.

were obtained in the crude esten f 'The highly purified isooctyl alcohol products,

number indicating a darkened,.l ow quality ester product. An ester product fhaving'a Hazen ester colorof 75 to 200 considered acceptable for commercial -use.

. This invention is. ases teat discovery that small amounts Oi certain phQsph rus esters can be very, effectively;..util ized'jforl obtaining very light colored to colorless e'stenproducts from 0x0 alcohols prepared in metallic reactors. The esters are added-in-small amounts relative to the amount of alcohol being used in the es- These esters which have been found effective maybe employed to give good results in metallic reactors of iron-generally, including mild steel and stainless steel.

, The phosphorusesters particularly preferred are those in which the phosphorus has a valence of three, that is, the phosphite esters.

sroupima xb fi y t-Y l k aralkyl' 0T cycloalkyl areuseful, and many 'of these com pounds are well known. in general, they may be; prepared by reaction ee ueame phosphorus halide with an alc'ohol or phenol for instance phosphorus trichloride.oigphosphorus tribromide.

Appropriate care should'be; taken to'. have the esters free of halogen andhalogen acidsto avoid, their corrosive effect. The aromatic type .phos-,

phite'esters have been found especially useful.

These include the triphenyl and tricresyl phos-r phites. The R groups of the esters may be sub-" stituted provided thegroup's do not cause an interference as to the color inhibting eifect or cause other undesirable side reactions.

;Another.,class of phosphite esters which can; be employed are thepolyphosphites, which are prepared by reacting the phosphorus halide with polyhydroxy compounds, thus producing chain typemolecules. In order to avoid a cross-linked insoluble'product, it is desirable to employ an agent in. the form of a monohydroxy compound.

Th'us mixtures of mono andipolyhydroxy com pounds are employed phite esters.

may be employed; however, care should be taken Although the sulfur content of the alcohol is not deleterious per se, the sulfurcomw. pounds-apparently. react in-some' manner "to. produce color bodies which impart a light yellow to a deep red color to the crudeester. that'is Thesimple phosphite esters, R3PO3, in which the R to prepare jthese. polyD Q f amounts than 0.10% do not satisfactorily prevent;

to hydrolyze the unesterifiedhalogen atoms of the. phosphorus halide to hydroxy in order ,to

avoidcorrosion during preparation of the --ester plasticizers in the metallic reactors.

In general, these esters are best employed in concentrations of fromdli) to 5%,;based on the. weightof alcohol used in the preparation of the plasticizers. The use of ..-large r amounts ,than' necessary is uneconomical and may give side re-:

actions and contamination, while smaller color formation during the. esterification.

Some phosphorus esters are; definitely'not festive. For instance, tricresylphosphate was found not to be effective in reduction of crude ester color in 5 Weight percent concentrations While it is not understood completely just how the preferred phosphites exercise .tlie beneficial-ti effect which they show with regard to suppressing color formation in the ester, it is believed that the organic phosphites are efiective as color inhibitors because they exercise an actualcolor inhibiting effect within the esterification reaction itself in the presence of the ,sulfur-c ontain-- ing impurities.

activity of the impurities may be inhibited by the It is possible that color forming reaction of the phosphites in some unknowni manner with the troublesome impurity compounds particularly those containing sulfur such as the mercaptan type.

The color improvement efiects of the organic phosphites occur whether the impurities are in the alcohol or acid intermediates used in the esterification.

It 'is particularly intended-as "a preferred em= bodiment of this invention that a'small amount? of the phosphite compounds be'included in the 5 OX0 alcohol products such as those'of the C1,? to.Ca range which are. to be used .to .e sterify' phthalic and similar acids to prepare esters for.

This incorporation of the phos-' plasticizers. I phites. in the alcohol is'an especially convenient method for insuring the-presence ofithe color. in-

hibitorand at thesafne time. forintroducing it.

into the metal prepared. Another particular reactor ,in which. the. ester is to.

ate "al ine. stats .1

is that the phosphite ester.ofthefialcohotbeing}; employed in the esterification can be employed as,

the color inhibiting material. alcoholicor phenolic material is introduced into the reaction zone.

Thus, no foreign' true in view of the fact that many organic phosticizers for resins and hence would so act when.

present in the ester to be used .as a plasticizer; Thus, these new inhibitors have the added advantagethat they do not even require removal from the final ester product as they arein no way detrimental to its action. Even though no metal surface is inactual, contact with the ester, it is considereddesirable to use a 'coloriinhibitoi' in esterificationsof sulfur-containing isooctyl alcohols especially where recycle alcohols are employed to any extent. I 1

The invention-will be described in more detail by the examples given below in which the good results obtained by theuse of variousuphosphite compounds are shownjby tli actual experimental testing.

proportion of it necessary for effective color suppression will do no harm when allowed to remain i in the final ester product. This is'particular1y--'.

ta obtained Tli'e-- 'polyphosphites were generally prepared by reactingonemoleof "a; phenolic material with one mole of PClz. 'Theresulting reaction product was further reactedwith one moleof' a-dihydroxy compound toproduce a moreorless linear type polyphosphite. The preparationanddetails of these compounds are more fully'described in copending application Serial No. 193,751, filed November 2, 1950. For instance, one pho'sphite 1 typematerial' was' prepared from parahydroxy diphenyl, 2,5 di-t-butyl hydroquinon'e and PCls to-give this. general type structure 'o-wfo toi s a J:

Inseam polyphosphiteNo. A.

a f EXAMPLE II 7 Similarly, "as described in Example I, polyphosphite type compounds may be preparedfrom.

a wide variety of aryland hydroquinone'type materials. A second compound prepared from alpha-ethyl-phenyl phenol, 2,5-di-t-butyl hydroquinone andPCls would have a type .structure as follows:

'1; O a: ffI'hiS latter material will .be designated. here! matter as polyphosphite lio. B.

will be designated hereinafter. as"

.. fur.

8;. EXAMPLE In For experimental purposes irflr testing "the" efficiency of phosphites in preventing; color. formation; the esterification reactions, tor ex? ample, a phthalylation' of'isooctyl'alcohol, were carried out loy:refluxing together parts by weightpf'a Ca isooctyl alcohol prepared bythe- 0x0 process with Z5parts' by weight of phthalic" anhydride togetherwith 1 part of Bureau of Standardsstainless'steel in a conventionalglass' esterification' reaction system. This .type' olf, ex"- periment was most "convenient and'quite' satise factory in lieu of the-use'of small scale stainless steel or metal. reactors which offer certain mechanical and technical .difilculties; The reactions were'carried out during a period .o'f'2hours atthe boiling point" of." the; mixture. The crude" esterification'. mixture was thenicooledand compared with Hazen' color standards. A complete description'ofithestandard Hazenestencolor-test-g is found in A. S.- T; M. D268-46.

'Experim'ents as described were carried out in;- which there.werepreparedesters 'of phthalicacidi by; reaction with an octyl alcohol derived byoxonation of a heptylenetifeed obtained by the U. 0. P. polymerizationof a C3-C4 olefin out from petroleum sources; In Table I below, there isree ported the data obtained when esterificationreactions were done using theabove described compounds A and B in amounts Off0.5WBight percent of'the polyphosphite based on thealcohol used" in the. esterification.

Table-1' USE OF POLYPHOSPHITES AS CGL'QRHNEHIBITQRH? It is "evident'from' Table I that .5 weightpercent of the polyphosphite compounds prepared as described iii/Examples A and Bwhenusedin an 0x0 alcohol giving very bad. ester color (2500 Hazen color value) when theesterification reaction is carried'out'in the presence of stainless steel, gives reduction in Hazen ester color tojvallls of to 160, which is at least equivalent to the ester colors obtained from alcohol from nonpetroleum sources, containing relativey no su EXAMPLEIV' Other types of organicphosphites may-also be used as color inhibitorsin esterifications'involv ing sulfur-containing alcohols particularly Cs isooctyl alcohols of 0x0 origin. Organic phosa phites oflthegeneral formula RaPOs whenadded in small amounts to.esterifications in which Oxdf alcohols. such was isoootyl alcohol are'bei'ng emf, ployedl .Crudeester products having a'colorrange ingv from light yellow to-water-White are obfl tained; concentrations of the phosphit'e compounds as low as 1%a're efiective.

.In Table II vbelow data are reported .on este'r ifications. which were conducted as. in Example,

and a reflux timeof .4 hours. 'Concentration'o f i 1% of tricresylphosphite was used as 'a jcolor ,75

formation inhibitor in run 2'.

Other triaryl phosphites are considered to be efiective as color inhibitors foresterifications using sulfur containing x0 alcohols. Other compounds which are members of this class include alkyl phosphites, mixed alkyl-aryl phosphites, and the isooctyl phosphites themselves.

EXAMPLE V Triphenyl phosphite has also been found to be efiectiveas a color inhibitor in esterifications in the presence of stainless steel- The experiments from which data are reported in Table III, were carried out in substantially the same,

manner as those of Example III.

Table III I I USE OF TRIPHEN'Y-LPHOSPHITE AS COLOR INHIBITOR It can be seen from Table III above that the purer vacuum distilled heart out isooctyl alcohol required substantially less of the triphenylphosphite as a color inhibitor than does plant quality isocctyl alcohol. Thus, a part but not all of the color-forming impurities were removed or rendered incapable of degradative color formation by the additional distillation of the alcohol.

EXAMPLE VI impurities. The excess isooctyl alcohol is unimportant. This phosphite product was added to an esterification carried out as described in Example III. The tri-isooctyl phosphite in concentration of .5 weight percent,based on the alcohol used, was found to decrease the Hazen ester color of the ester product in comparison to the value of the ester color prepared in a reaction t which no phosphite was added.

Table IV USE OF TRI-ISOOCTYLPHOSPHITE AS COLOR INHIBITOR Tri-isooctyl- Ester Run N 0. Alcohol phosphite, Hazen wt. percent Colors 1 0| 0x0 alcohol None 1, 475 2 do 5 450 file of this patent:

UNITED STATES PA'I'F..I\TTSv Number Name Date 1,948,281 Smith Feb. 20, 1934 1,993,737 Graves Mar. 12, 1935 2,164,188 Groll -1 June 27, 1939 2,197,546 Baxter Apr. 16, 19,40

' FOREIGN PATENTS Number Country Date 588,833 Great Britain June 4, 1947 10 What is claimed is: 1. A process for the preparation of organic esters in the presence of stainless steel surfaces from a dibasic organic acid of the group consisting of maleic, adipic, and phthalic acids and a monohydric alkanol having 4 to 12 carbon atoms per molecule having sulfur-containing impurities which cause color formation unless inhibited during the esterification, said alkanol being produced in a two-stage operation consisting of a first stage in which hydrogen, carbon-monoxide, and an olefin arev contacted in the presence of an oxonation catalyst, forming a product predominantly aldehyde and of a second stage in which the said aldehyde product is catalytically reduced with hydrogen to form the corresponding alkanol which comprises carrying out the esterification of the alcohol having the sulfur-containing impurities in the presence of from "0.10 to 5 weig'ht percent based on the alcohol of an organicphosphite ester from the group consisting of trialkyl phosphite, triphenyl phosphite, tricresyl phosphite, and organic homocyclic polyphosphite ester to inhibit color formation during the esterification, and obtaining a relatively colorlessorganic ester product from the esterification.

'2. A process for the preparation of phthalic esters in the presence of stainless steel surfaces from phthalic acid and an iso-octyl alcohol having sulfur-containing impurities which cause color formation during the esterification unless inhibited, said alcohol being produced in a twostage operation consisting of a first stage in which hydrogen, carbon monoxide, and an olefin are contacted in the presence of an oxonation catalyst, forming a product predominantly aldehyde and of a second stage in which the said aldehydeproduct is catalytically reduced with hydrogenfto form the corresponding alcohol which comprises incorporating in the alcohol from 0.10 to 5 weight percent based on the alcohol of an organic phosphite ester from the class consisting of trialkyl phosphite, triphenyl phosphite, tricresyl phosphite, and organic homocyclic polyphosphite esters, and heating a mixture of the alcohol containing said impurities and the-organic phosphite ester with the phthalic acid to a boiling temperature for a period of about two hours in the presence of stainless steel surfaces to obtain a relatively colorless phthalate ester.

3. A process as described in claim 1 in which the phosphite ester is triphenyl phosphite.

4. A process as described in claim 1 in which the phosphite ester is tricresyl phosphite.

5. A process as described in claim 1 in which the phosphite ester is an organic homocyclic polyphosphite ester.

BOYD E. HUDSON, JR.

HOWARD L. WILSON.

JOSEPH F. NELSON.

REFERENCES CITED The'following references are of record in the 

1. A PROCESS FOR THE PREPARATION OF ORGANIC ESTERS IN THE PRESENCE OF STAINLESS STEEL SURFACES FROM A DIBASIC ORGANIC ACID OF THE GROUP CONSISTING OF MALEIC, ADIPIC, AND PHTHALIC ACIDS AND A MONOHYDRIC ALKANOL HAVING 4 TO 12 CARBON ATOMS PER MOLECULE HAVING SULFUR-CONTAINING IMPURITIES WHICH CAUSE COLOR FORMATION UNLESS INHIBITED DURING THE ESTERIFICATION, SAID ALKANOL BEING PRODUCED IN A TWO-STAGE OPERATION CONSISTING OF A FIRST STAGE IN WHICH HYDROGEN, CARBON-MONOXIDE, AND AN OLEFIN ARE CONTACTED IN THE PRESENCE OF AN OXONATION CATALYST, FORMING A PRODUCT PREDOMINANTLY ALDEHYDE AND OF A SECOND STAGE IN WHICH THE SAID ALDEHYDE PRODUCT IS CATALYTICALLY REDUCED WITH HYDROGEN TO FORM THE CORRESPONDING ALKANOL WHICH COMPRISES CARRYING OUT THE ESTERIFICATION OF THE ALCOHOL HAVING THE SULFUR-CONTAINING IMPURITIES IN THE PRESENCE OF FROM 0.10 TO 5 WEIGHT PERCENT BASED ON THE ALCOHOL OF AN ORGANIC PHOSPHITE ESTER FROM THE GROUP CONSISTING OF TRIALKYL PHOSPHITE, TRIPHENYL PHOSPHITE, TRICRESYL PHOSPHITE, AND ORGANIC HOMOCYCLIC POLYPHOSPHITE ESTER TO INHIBIT COLOR FORMATION DURING THE ESTERIFICATION, AND OBTAINING A RELATIVELY COLORLESS ORGANIC ESTER PRODUCT FROM THE ESTERIFICATION. 